Electric motor with heat dissipation for the motor shaft bearing

ABSTRACT

The invention relates to an electric motor with a motor housing ( 2 ) which has a shaft section for receiving a motor shaft ( 4 ) and a motor section for receiving motor electronics ( 5 ) and motor windings ( 6 ), wherein the shaft section and the motor section are separated from each other in a sealed manner by a separating pot ( 7 ) arranged in the motor housing ( 2 ), wherein, in the separating pot ( 7 ), a metal ball bearing pot ( 8 ) is arranged, in which a ball bearing ( 9 ) is fixed, and wherein the ball bearing pot ( 8 ) lies indirectly against a motor housing section which is connected to the outer surroundings, via the separating pot ( 7 ), such that the motor housing functions as a cooling body, and heat generated by the ball bearing ( 9 ) during operation is dissipated onto the motor housing and the outer surroundings via the ball bearing pot ( 8 ) and the separating pot ( 7 ).

The invention relates to an electric motor of compact design with heat dissipation for the motor shaft bearing.

In electric motors which generate a high rotational speed of the motor shaft, the power dissipation of the ball bearing in which the motor shaft is mounted considerably increases due to strong heat development. Especially in compact designs of the electric motor, in which the ball bearing is arranged directly adjoining numerous other components, the generated heat cannot be dissipated to a sufficient extent.

Therefore, the underlying aim of the invention is to provide, in an electric motor, improved heat dissipation for the ball bearing in which the motor shaft is mounted.

This aim is achieved by the combination of features according to claim 1.

According to the invention, an electric motor with a motor housing is proposed, which has a shaft section for receiving a motor shaft and a motor section for receiving motor electronics and motor windings. The shaft section and the motor section are separated in a sealed manner from one another by a separating pot arranged in the motor housing, wherein, in the separating pot, a metal ball bearing pot is arranged, in which a ball bearing is fixed. The ball bearing pot lies indirectly against a motor housing section which is connected to the outer surroundings, via the separating pot, such that the motor housing functions as cooling body and heat generated by the ball bearing during operation is dissipated onto the motor housing and the outer surroundings via the ball bearing pot and the separating pot.

The separating pot is used in order to separate the shaft section and the motor section and to prevent gas exchange between crankcase and electronics or motor windings.

However, the separating pot with the ball bearing pot arranged therein leads to a design in which the ball bearing has to be arranged highly centrally packed and is able to dissipate little of the heat generated during operation. According to the invention, the heat dissipation onto the motor housing occurs due to a connection of the separating pot and the ball bearing pot to the ball bearing received therein.

In an embodiment variant of the electric motor, it is provided that the separating pot is formed as a single piece through the motor housing around a rotation axis of the motor shaft. In particular, the motor housing forms a circumferential outer wall which, on an axial side, is adjoined by an axial wall into which the separating pot is sunk. The separating pot is preferably designed in the shape of a hollow cylinder with sections of different diameter, wherein the ball bearing pot is arranged in the section of the ball bearing pot axially protruding farthest into the motor housing.

Here, an advantageous embodiment is one in which the separating pot and the ball bearing pot are designed to be of identical shape in the section of the separating pot in which the ball bearing pot is arranged. In other words, the ball bearing pot and the separating pot determine the same outer contours.

An advantageous embodiment of the electric motor is moreover one in which a heat sink paste is provided between the separating pot and the section of the motor housing which is indirectly connected to the ball bearing pot via the separating pot. The heat sink paste preferably forms an intermediate layer and provides a heat connection of the motor housing to the separating pot, without the components touching. Thus, vibrations of the individual components remain uncoupled from one another.

A development of the electric motor is characterized in that the motor housing has a detachable housing cover which can be put on an axial side of the remainder of the motor housing and which forms the section of the motor housing which is indirectly connected to the ball bearing pot and therefore the ball bearing via the separating pot. To the extent that the separating pot forms a single piece with the motor housing, the mounting of the components of the electric motor can occur via the side axially facing the separating pot, on which side the housing cover is removably positioned. At the same time, the solution with a housing cover as cooling body provides a large surface for heat dissipation.

The performance of the heat dissipation is further improved in the electric motor in a variant in which the housing cover has a cooling element protruding axially in the direction of the ball bearing pot, which locally increases a surface for connection to the ball bearing pot indirectly via the separating pot.

As an advantage embodiment, it is provided that the cooling element is designed to be of cylindrical or conical shape with an axial surface for connection to an axial outer wall of the separating pot. Thus, the heat of the ball bearing is transmitted from the ball bearing pot to the separating pot, then further from the axial outer wall surface thereof to the connection surface of the cylindrical cooling element, and finally to the entire surface of the housing cover.

In a preferred embodiment, the ball bearing pot forms a ball bearing seat into which the ball bearing is pressed.

In addition, a variant of the electric motor is characterized in that the ball bearing pot has a free space between the ball bearing and the section of the motor housing which is connected to the outer surroundings. The ball bearing can thus directly dissipate heat to the air into the free space and is not directly connected to the axial surface of the ball bearing pot which adjoins the separating pot and the cooling body.

Furthermore, in the electric motor, in a development, it is provided that the separating pot extends axially through the motor housing up to the housing cover. The separating pot thus determines, in axial direction, i.e., along the rotation axis of the motor shaft, a considerable portion of the centrally internal motor housing around the rotation axis. Preferably, the separating pot extends in axial direction over 60-95%, more preferably over 70-95%, furthermore preferably over 80-90% of the total axial extent of the motor housing.

An advantageous embodiment example is moreover one in which the motor housing and the separating pot are made of plastic and the metal ball bearing pot is directly overmolded with plastic in the injection molding process.

For a compact design, in the electric motor, it is advantageously provided that the windings enclose the separating pot in circumferential direction. At the same time, it is advantageous that the windings are arranged axially spaced from the ball bearing. Thus, the heat development of the motor windings remains separated from the heat development of the ball bearing.

It is also advantageous for a compact design of the electric motor that the motor electronics is arranged on a circuit board which has a central opening, and the cooling element protruding from the housing cover extends through the central opening. Alternatively to this, it is provided that the separating pot extends through the central opening. Furthermore, alternatively, the heat dissipation can also occur directly via the circuit board. Then, the central opening can also be dispensed with.

Other advantageous developments of the invention are characterized in the dependent claims and represented in further detail together with the description of the preferred embodiment of the invention in reference to the figures. In the drawings:

FIG. 1 shows a lateral cross-sectional view through an electric motor of an embodiment example;

FIG. 2 shows a detail view from FIG. 1.

In FIGS. 1 and 2, an embodiment example of an inventive electric motor 1 is represented in a lateral cross-sectional view and a detail view, respectively.

The electric motor 1 comprises the single-piece motor housing 2 with the housing cover 3 which can be axially fixed in a detachable manner on the motor housing 2 and which, in the fixed state, forms a part of the motor housing. On the side axially facing the housing cover 3, the motor housing 2 forms, as a single piece, the separating pot 7 extending into the interior of the motor housing 2. Between the inner wall of the motor housing 2 and the outer shell of the separating pot 7, the motor section is located, in which the motor windings 6 and the motor electronics 5 fixed on the circuit board 14 are received. Sealingly delimited via the separating pot 7, the shaft section, in which the motor shaft 4 extends along the rotation axis thereof, is located within the separating pot 7. The separating pot 7 extends in axial direction substantially through the entire motor housing 2 up to the housing cover 3.

In the deepest section of separating pot 7, when viewed in axial direction, the ball bearing pot 8 made of a heat conducting material, in particular metal, is arranged. The motor housing 2 with the separating pot 7 is injection molded with plastic around the ball bearing pot 8 in the injection molding process, so that the separating pot 7 and the ball bearing pot 8 have the same shape or inner and outer contours and directly adjoin one another. The ball bearing pot 8 determines the bearing seat for the pressed-in ball bearing 9 in which the motor shaft 4 is mounted. Between the ball bearing 9 and the axial inner wall surface of the separating pot 7, the free space 13 is formed, into which the motor shaft 4 extends with by means of its free end.

Around the rotation axis, on the housing cover 3, designed in such a manner as to form a single piece, is a cooling element 11 in the form of a cylinder made of solid material, protruding axially in the direction of the ball bearing pot 8. A layer of the heat sink paste 10 is provided axially between the cooling element 11 and the axial outer wall surface of the separating pot 7.

The heat dissipation of the heat generated during operation by the ball bearing 9 occurs from the ball bearing 9 onto the ball bearing pot 8, further onto the separating pot 7 and in axial direction via the heat sink paste 10 onto the cooling element 11 of the housing cover 3 of the motor housing 2. From the housing cover 3, the heat is dissipated further into the outer surroundings. The motor housing and in particular the housing cover 3 thereof therefore function as cooling body. In an alternative embodiment, not shown, the heat sink paste 10 is dispensed with and the cooling element 11 is in direct contact with the separating pot 7.

The separating pot 7 is hollow cylindrical and subdivided into three axial sections each with different inner diameters. In the region of the smallest diameter, the free space 13 is arranged, in the central region, the bearing seat with the ball bearing 9 is arranged, and in the region of the largest inner diameter, the motor windings 6 are arranged radially around the separating pot 7. The ball bearing 9 thus has no overlap with respect to the motor windings 5, when viewed in axial direction.

The circuit board 14 determines, around the rotation axis of the motor shaft 4, the central opening 15, through which, in axial direction, the cooling element 11 axially protruding from the housing cover 3 extends through to the separating pot 7. In an alternative variant, not represented, instead of the cooling element 11, the region of smallest diameter of the separating pot 7 can extend through the opening 15, so that the contact between separating pot 7 and cooling element 11 occurs axially above the circuit board 14. It can also be provided to design the housing cover 3 without a cooling element 11 and to move the separating pot 7 directly or via the heat sink paste 10 against the axial inner wall of the housing cover 3. 

1. An electric motor with a motor housing (2) which has a shaft section for receiving a motor shaft (4) and a motor section for receiving motor electronics (5) and motor windings (6), wherein the shaft section and the motor section are separated from each other in a sealed manner by a separating pot (7) arranged in the motor housing (2), wherein, in the separating pot (7), a metal ball bearing pot (8) is arranged, in which a ball bearing (9) is fixed, and wherein the ball bearing pot (8) lies indirectly against a motor housing section which is connected to the outer surroundings, via the separating pot (7), such that the motor housing functions as a cooling body and heat generated by the ball bearing (9) during operation is dissipated onto the motor housing and the outer surroundings via the ball bearing pot (8) and the separating pot (7).
 2. The electric motor according to claim 1, characterized in that the separating pot (7) is formed as a single piece through the motor housing (2) around a rotation axis of the motor shaft (4).
 3. The electric motor according to claim 1 or 2, characterized in that the separating pot (7) and the ball bearing pot (8) are designed to be of identical shape in the section of the separating pot (7) in which the ball bearing pot (8) is arranged.
 4. The electric motor according to any one of the preceding claims, characterized in that, between the separating pot (7) and the motor housing section (2) which is indirectly connected to the ball bearing pot (8) via the separating pot (7), a heat sink paste (10) is provided.
 5. The electric motor according to any one of the preceding claims, characterized in that the motor housing has a detachable housing cover (3) which can be put on an axial side of the remainder of the motor housing (2) and which forms the section of the motor housing which is indirectly connected to the ball bearing pot (8) via the separating pot (7).
 6. The electric motor according to the preceding claim, characterized in that the housing cover (3) has a cooling element (11) protruding axially in the direction of the ball bearing pot (8), which locally increases a surface for connection to the ball bearing pot (8) indirectly via the separating pot (7).
 7. The electric motor according to the preceding claim, characterized in that the cooling element (11) is designed to be of cylindrical or conical shape with an axial surface for connection to an axial outer wall surface of the separating pot (7).
 8. The electric motor according to any one of the preceding claims, characterized in that the ball bearing pot (8) forms a ball bearing seat into which the ball bearing (9) is pressed or inserted.
 9. The electric motor according to any one of the preceding claims, characterized in that the ball bearing pot (8) has a free space (13) between the ball bearing (9) and the section of the motor housing (2) which is connected to the outer surroundings.
 10. The electric motor according to any one of the preceding claims 5 to 9, characterized in that the separating pot (7) extends axially through the motor housing (2) up to the housing cover (3).
 11. The electric motor according to any one of the preceding claims, characterized in that the motor housing (2) and the separating pot (7) are made of plastic, and the metal ball bearing pot (8) is directly overmolded with the plastic.
 12. The electric motor according to any one of the preceding claims, characterized in that the motor windings (6) enclose the separating pot (7) in circumferential direction and are arranged axially spaced from the ball bearing (9).
 13. The electric motor according to any one of the preceding claims 5 to 12, characterized in that the motor electronics (5) is arranged on a circuit board (14) which has a central opening (15), and in that the cooling element (11) protruding from the housing cover (3) extends through the central opening (15).
 14. The electric motor according to any one of the preceding claims 5 to 12, characterized in that the motor electronics is arranged on a circuit board which has a central opening, and in that the separating pot (7) extends through the central opening. 